Endocrinology of Menopause
Sexual hormones are steroïd hormones and have a similar chemical structure and mechanism of activity. After binding to a specific receptor, they change the functioning of the genome.
Classes are corticoïsteroids en sex steroiden such as androgens, oestrogens and progestagens.
Each subgroup indicates a series of hormones with a similar effect. Estrogens comprise the natural hormones such as oestradiol, oestrone and oestriol, eventually with slight chemical alterations to increase solubility in water for oral administration, such as ethinylestradiol or oestradiol-valerianate. Animals and plants have other oestrogens, such as in the urine of pregnant mares and Phyto oestrogens. Important is the confusion of the word ‘natural’: Fyto estrogens occur in nature but are not natural for women - oestradiol-valerianate is chemically modified but becomes a natural estrogen in blood.
Oestrogens induce the development of breasts and the uterus and the development of the endometrium. Progesterone changes the estrogen effect on the endometrium and stops growth while preparing for a pregnancy.
Oestrogens and progesterone originate from the ovary and are linked to ovulation. Male hormones are made in the ovary and in the adrenals.
Important is that ‘so called’ normal concentrations are a range and that concentrations in the individual woman can be much higher of lower. This explaind that individualisation of therapy is needed
The menstrual cycle
The menstrual cycle is similar to a domino cascade: a growing oocyte starts a cascade of events with strict timing, which explains that a menstrual cycle can be so regular at 28 days.
Estrogens increase in parallel with the growing follicle, then induce ovulation and thereafter secretion of progesterone. In the absence of a pregnancy, progesterone secretion stops after 14 days, and this decrease induces a menstruation.
Important aspects to know for hormone replacement therapy
- Oestrogens stimulate the growth of the endometrium
- Progesterone stops the growth, also if given together with estrogens
- A sudden drop in oestrogens or progestagens induces withdrawal bleeding.
- less bleeding if the endometrium is thin.
Oocytes
The secretion of estrogens and progestagens is linked to the follicular growth At 50 years of age, few oocytes are left, and ovulation and hormone production stops.
Puberty versus Menopause
At puberty starts, the secretion of androgens from the adrenals and ovaries, inducing hair growth of the pubis, and somewhat later estrogens induce breast development and menstruation.
In the absence of follicular growth and ovulation, menopause starts; However, the androgen secretion continues explaining that pubic hair does not disappear. Androgens can be metabolised into estrogens.
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